Mycobacterium szulgai is a rare nontuberculous mycobacterium found in Korea. It is an opportunistic pathogen and is usually isolated from patients with a history of alcoholism, chronic pulmonary disease, or an immunocompromising condition. We present here a case of M. szulgai isolated from a patient with a history of pulmonary tuberculosis. A 54-year-old man was admitted with dyspnea and febrile sensation. He had a history of pulmonary tuberculosis which occurred 30 years earlier and treatment with anti-tuberculosis medication. His chest computed tomography scan showed cavitary consolidation in both upper lungs. A sputum acid-fast bacilli (AFB) smear was positive and anti-tuberculous medication was started. However, a polymerase chain reaction for mycobacterium tuberculosis was negative and anti-tuberculous medication was stopped. M. szulgai was isolated on 3 separate sputum and bronchial wash fluid AFB cultures. He was treated with clarithromycin, rifampicin, and ethambutol. After 1 month, a sputum AFB smear and culture became negative and no additional M. szulgai were isolated during a 16-month treatment.